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Wiki source code of WebObjects with Scala

Version 93.1 by Ravi Mendis on 2009/09/17 23:12
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1 === What is Scala? ===
2
3 Scala is a modern language not unlike Groovy.
4 It is said to be more powerful (and faster) than Groovy or Ruby which has been the reason for its adoption at sites like Twitter.
5
6 Many of its features and paradigms favor multi-threading and concurrency. Some of these may not be unfamiliar to Objective-C and WebObjects developers. Here's a summary:
7
8 |= |= Objective-C |= Java |= Scala
9 |= Mutable/Immuable Datatypes | Collections //e.g: NSArray/NSMutableArray// | No | Yes
10 |= Closures | Blocks (//Extension//) | No | Yes
11 |= Static variables | Yes | Yes | No
12 |= Static methods/functions | Yes | Yes | No
13 |= Concurrency | [[Grand Central Dispatch>>http://en.wikipedia.org/wiki/Grand_Central_Dispatch]] (//Extension//)| //Threads// |[[Actors>>http://en.wikipedia.org/wiki/Actor_model]]
14 |= |= Weakly Typed |=--Strongly Typed--|= Strongly Typed
15
16 Other notable features include:
17
18 |= |= Objective-C |= Java |= Scala
19 |= Parametered methods | Yes //e.g: addObject: to~:// | No | Yes //e.g: add(object= ,to=)//
20 |= Class composition | Categories | Interfaces | Traits
21
22 A fuller description of Scala can be found [[here>>http://en.wikipedia.org/wiki/Scala_(programming_language)]].
23
24 === Why Use Scala? ===
25
26 With Web 2.0, building concurrent WebObjects applications is a must.
27 Developing and maintaining a concurrent or multi-threaded WebObjects application can be challenging.
28
29 Scala offers concurrency that is (effectively) built-in to the language and is inherently thread-safe.
30
31 In other words, developing Ajax (i.e asynchronous communication) with WO will require concurrent request handling and thread-safe code, for which Scala is a better choice than Java.
32
33 In addition it may offer new solutions for concurrency in WebObjects.
34
35 === Can WebObjects be Programmed In Scala? ===
36
37 Yes. It is very simple.
38 Scala compiles to java bytecode. Hence using it with WebObjects is fairly straightforward.
39
40 = WebObjects In Scala =
41
42 The following highlights some of the differences between Java and Scala in WebObjects:
43
44 == EOs in Scala ==
45
46 === Thread-Safe Shared Vars ===
47
48 Scala doesn't have static variables or methods. However, a class can have a //Companion Object// that will allow you to achieve something equivalent to static variables.
49 One of the advantages of this approach is that it is **thread-safe**, so you don't have to worry about synchronizing access to these fields in a concurrent application.
50
51 In Java:
52
53 {{code}}
54
55 public class _Talent extends EOGenericRecord {
56 public static final String ENTITY_NAME = "Talent";
57
58 {{/code}}
59
60 In Scala:
61
62 {{code}}
63
64 object _Talent extends EOGenericRecord {
65 val ENTITY_NAME = "Talent"
66
67 {{/code}}
68
69 ==== Compacted imports ====
70
71 Two lines in Java is compacted into one in Scala.
72
73 In Java:
74
75 {{code}}
76
77 import com.webobjects.eocontrol.EOGenericRecord;
78 import com.webobjects.eocontrol.EORelationshipManipulation;
79
80 {{/code}}
81
82 In Scala:
83
84 {{code}}
85
86 import com.webobjects.eocontrol.{EOGenericRecord, EORelationshipManipulation}
87
88 {{/code}}
89
90 == WOComponents in Scala ==
91
92 ==== Compact Constructors ====
93
94 Scala allows for simpler use of multi-valued constructors than Java.
95
96 In Java:
97
98 {{code}}
99
100 public class MenuHeader extends WOComponent {
101
102 public MenuHeader(WOContext aContext) {
103 super(aContext);
104 }
105
106 {{/code}}
107
108 In Scala:
109
110 {{code}}
111
112 class MenuHeader(context: WOContext) extends WOComponent(context: WOContext) {
113
114 {{/code}}
115
116 ==== Simplified Exception Handling ====
117
118 Scala doesn't force you to catch exceptions unlike in Java.
119 In addition, the syntax employs Scala's very powerful pattern matching to handle different exceptions.
120
121 In Java:
122
123 {{code}}
124
125 try {
126 EditPageInterface epi = D2W.factory().editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session());
127 epi.setNextPage(context().page());
128 nextPage = (WOComponent) epi;
129 } catch (IllegalArgumentException e) {
130 ErrorPageInterface epf = D2W.factory().errorPage(session());
131 epf.setMessage(e.toString());
132 epf.setNextPage(context().page());
133 nextPage = (WOComponent) epf;
134 }
135
136 {{/code}}
137
138 In Scala:
139
140 {{code}}
141
142 try {
143 var epi: EditPageInterface = D2W.factory.editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session)
144 epi.setNextPage(context.page)
145 nextPage = epi.asInstanceOf[WOComponent]
146 } catch {
147 case e: IllegalArgumentException => {
148 var epf: ErrorPageInterface = D2W.factory.errorPage(session)
149 epf.setMessage(e.toString)
150 epf.setNextPage(context.page)
151 nextPage = epf.asInstanceOf[WOComponent]
152 }
153 }
154
155 {{/code}}
156
157 == How to Add Scala to a WO Project ==
158
159 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
160
161 {{note title="Note"}}
162
163 This is for Eclipse/WOLips IDE
164
165 {{/note}}
166
167 == WO Scala Example ==
168
169 The following example is a mixed Java/Scala version of the WO Movies D2W app.
170 All the EO logic and WO components are in Scala.
171 Only the Application class is Java.
172
173 {{attachments patterns=".*zip"}}{{/attachments}}
174
175 === Setup ===
176
177 1. [[Install the Scala eclipse IDE>>http://www.scala-lang.org/node/94]]
178 1. Install and run the OpenBase OBMovies database.
179 1. Right-click on Application.java and run as a WOApplication (as usual).
180
181 ==== EO Templates ====
182
183 See: [[Scala templates>>http://wiki.objectstyle.org/confluence/display/WOL/EOGenerator+Templates+and+Additions]]
184
185 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
186
187 1. Change the File Names Extension to "scala"
188 1. Uncheck Java under Options